Spatial correlation structures of CPT data in a liquefaction site

[[abstract]]In this paper the spatial structures of cone penetration test parameters in a liquefaction site in Taiwan are estimated based on multiple CPTs conducted in-situ. The study area was divided into three sub-regions based on the geological condition of the study area. The results show that in the vertical profile, cone tip resistance (q(c)) has a larger scale of fluctuation (SOF) than that of sleeve friction (f(s)). The soil profile which is composed of various sources and complex process of deposition has a smaller SOF in q(c) parameter. However, the spatial structure in f(s) parameter is not sensitive to the geological formation. The analysis results of the CPT data in horizontal direction indicate that the correlation distances of q(c) and f(s) in horizontal direction are similar. The horizontal spatial structure is dominated by the anisotropy of the geological and river systems. in conclusion, this study demonstrates that a proper geological zonation is necessary for estimating the spatial structure in both the vertical and horizontal directions. (C) 2009 Elsevier B.V. All rights reserved.[[note]]SC

Stress distribution and development within geosynthetic-reinforced soil slopes

[[abstract]]Numerical methods combined with centrifuge tests are used to investigate the distribution and development of soil stresses and reinforcement tensile loads in geosynthetic-reinforced soil (GRS) structures. In this study, system stability indicated by the factor of safety (FS) of GRS slopes is calculated by limit equilibrium analysis. Stress information under various stress states is evaluated using finite element analysis. Advanced models and an integration algorithm are implemented in finite element code to enhance the simulation results. The proposed numerical models are validated by centrifuge tests of two GRS slopes with different backfill densities. Numerical results indicate that soil stress mobilisation can be described by the soil stress level S, which is defined as the ratio of the current stress status to peak failure criteria. For both slope models, as loading increases, backfill stresses develop and propagate along the potential failure surface. Mobilisation of soil stress was non-uniform along the failure surface. Immediately after the stress level reaches peak (S = 1), strength softening initiates at the top and toe of the slope at approximately FS = 1.2. The slope settlement rate and reinforcement tensile load increase significantly when soil softening begins. The softening occurs randomly and irregularly along the failure surface, and the formation of the soil-softening band completes at approximately FS = 1.1. The failure surface corresponds to the locus of intense soil strains and the maximum tensile loads at each reinforcement layer. Additionally, the numerical results show that the initiation of soil softening and the failure of the slope occurred earlier in the slope model with low backfill density. The numerical results support the view that peak shear strength, not residual shear strength, governs system stability. Last, the distribution of maximum reinforcement tensile loads with depth was highly uniform at low g-level and became trapezoidal at high g-level. The peak value was located at approximately mid-height of the reinforced slopes. This observation contradicted the triangular distribution with depth assumed in current design methodologies for geosynthetic structures.[[note]]SC

Study of the mechanical compression behavior of municipal solid waste by temperature-controlled compression tests

[[abstract]]Understanding the compression behavior of waste materials is important to the operation and rehabilitation of waste landfill sites. Nevertheless, predicting this behavior is extremely difficult because waste materials are heterogeneous and highly biodegradable. In terms of the mechanism, waste settlement comprises mechanical and biodegradation compressions. This research performs a series of tests to study the mechanical compression behavior of waste materials by using a specifically designed testing device. The device has the ability to keep the temperature low enough to impede the biodegradation of organics, thereby allowing the mechanical compression behavior to be determined. In general, the observed mechanical compression indicates that municipal solid waste (MSW) is very compressible. As the load increases, MSW becomes less compressible because the waste is getting denser. MSW also has a very large creep compression rate, whereby the coefficient of compression of the primary phase is only about 2-8 times that of the creep phase. The magnitude of loading and the elapsed time of loading affect the mechanical compression behavior of MSW. The effects of some parameters on the mechanical behavior are studied herein. MSW with higher dry density had a smaller compressibility. Higher water content also led to a higher compression rate in the primary and creep phases. The waste containing more compressible constituents compressed to a larger extent but with an insignificant increase in the compression rate. The biodegradation of organic constituents did not influence the mechanical compression behavior significantly but increased the rate of creep compression notably. This research also developed a regression relationship between the coefficient of volume compressibility and the dry density of the waste. The prediction of mechanical compression in a field case validated the application of this regression relationship.[[note]]SC

Effects of strong ground motion on the susceptibility of gully type debris flows

[[abstract]]Typhoon Herb in 1996 caused widespread debris flows in central Taiwan. The 7.3 Chi-Chi earthquake on September 21,1999, which also took place in central Taiwan, induced many landslides in the region. These landslides turned into debris flows when Typhoon Toraji struck Taiwan in 2001. This research selects three regions which suffered a ground motion class of 5, 6, and 7 on the Richter scale during the Chi-Chi earthquake as study areas. Air photos from 1997 and 2001 of these regions are used to map the gully-type debris flows that took place after Typhoons Herb and Toraji, respectively. The gullies adjacent to the debris flow, but without a trace of debris flows, are also mapped as the non-debris flow data. The topography, hydrogeology, and rainfall factors - where debris flow occurred and in which there was no occurrence of debris flows in these gullies were retrieved from DTM, geological maps, and iso-countour maps, and of rainfall through GIS processing. These characteristic are introduced into a probabilistic neural network to build a predicting model for the probability of the occurrence of debris flows. Three series of cross analyses are conducted to compare the probability of the occurrence of debris flows of the same dataset predicted by different prediction models. The results reveal that the susceptibility of debris flows was elevated after the Chi-Chi earthquake struck. The upsurge of susceptibility was more obvious for the regions that received a higher class of ground motion. (C) 2008 Elsevier B.V. All rights reserved.[[note]]SC

Large scale direct shear tests of soil/PET-yarn geogrid interfaces

[[abstract]]The interface shear strength of soil against geosynthetic is of great interest among the researchers in geosynthetic properties. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of different soils (sand, gravel, and laterite) against PET-yarn geogrids of various tensile strengths, percent open area, and aperture patterns. First, the appropriateness of different set-ups of a lower shearing box is examined in this study. It reveals that a lower box which is filled with the test soil and is of the same size as the upper box is more suitable for testing the soil/geogrid interface. The test results show that the soil/PET-yarn geotextile interface has significantly lower shear strength than soil strength. The ratio of shear strength soil/PET-yarn geotextile interface to internal shear strength of soil is about 0.7-0.8 for Ottawa sand and for laterite, and it is about 0.85-0.95 for gravel. On the other hand, the soil/geogrid interface has higher shear strength. The ratio of shear strength soil/PET-yarn geogrid interface to internal shear strength of soil is about 0.9-1.05. It is found that the shear strength ratio of soil/PEr-yarn geogrid interface is positively correlated to the transverse tensile strength of the PFT-yarn geogrid. However, it is negatively correlated with the aperture length and percent open area of the PET-yarn geogrid. The interface shear test results of PET-yarn geogrid against different soils are compared with the test results predicted by a classical model for analyzing the applicability of the classical model. Further, a simple model is proposed herein to estimate the bearing resistance provided by the transverse ribs of geogrid. It shows this component to be about 0-15% when PET-yarn geogrid is against Ottawa sand or laterite, while it is smaller when the PET-yarn geogrid is against gravel. (C) 2008 Elsevier Ltd. All rights reserved.[[note]]SC

Calibration of liquefaction potential index: A re-visit focusing on a new CPTU mode

[[abstract]]This paper presents a review of the state-of-the-art of Liquefaction Potential Index (LPI), a parameter created by Iwasaki and his co-workers to characterize the potential for surface manifestation of liquefaction, and the results of an extensive calibration of the LPI with a focus on a new model based on piezocone testing (CPTU). The results show that the threshold criteria developed by Iwasaki and his co-workers for interpreting the calculated LPI are not universally applicable. To the contrary, the LPI must be re-calibrated when any component model of the LPI framework is replaced with a new model. The new CPTU model is a significant advance in the cone penetration-based liquefaction evaluation; in fact, it is the first simplified model that explicitly incorporates pore pressure measurement as one of its input parameters. This CPTU model is applicable to a wide range of soil types and thusly enables a more convenient and effective modeling of liquefaction effects within the LPI framework. Probabilistic characterization of the new CM model is carried out. Finally, the results of the calibration of the LPI calculated with this CPTU model, along with the concept of the probability of surface manifestations, are presented and discussed. (C) 2008 Elsevier B.V. All rights reserved.[[note]]SC

Graphical solutions for estimating geosynthetic loads in geosynthetic-soil layered systems on slopes

[[abstract]]This paper presents graphical solutions for estimating geosynthetic loads in geosynthetic - soil layered systems on slopes. The graphical solutions are based on a simple analytical approach that maintains strain compatibility and force equilibrium. The solutions are presented graphically using dimensionless terms that incorporate the loading conditions and material properties. An illustrative example is provided to demonstrate how the graphical solutions are used.[[note]]SC

Lessons learned from three failures on a high steep geogrid-reinforced slope

[[abstract]]An excavated slope that connects the school campus and Tai-21 Road is located on the approaching road to Chi-Nan University in Nantou, Taiwan. The toe portion of this high and steep slope is reinforced by a PET geogrid, with the height of the reinforced zone ranging between 10 meters (m) and 40 m at different sections. A slope failure occurred during construction of the reinforced slope in 1994. A massive failure of the reinforced slope then happened at the 40 m high section when the Chi-Chi (Taiwan) earthquake struck on September 21, 1999. The failure portion was rehabilitated, but another failure of the reinforced slope took place at another 20 m high section after a heavy rainstorm on July 2, 2004. The research herein presents the information and the history of these PET geogrid-reinforced slope failures. We perform extensive field observations and numerical analyses to examine the failure mechanism and causes contributing to these failures. Lessons learned from these case histories, with regard to carrying Out a detailed site investigation, selecting permeable materials as backfill, installing drainage systems appropriately and combining the design of a reinforced slope with other types of retaining structures to improve the system global stability, are also discussed. (C) 2012 Elsevier Ltd. All rights reserved.[[note]]SC